An aqueous vinyl resin emulsion prepared by an emulsion polymerization of .alpha.,.beta.-ethylenically unsaturated compounds as vinyl acetate, vinyl chloride, vinylidene chloride, acrylic monomer and the like, in an aqueous medium in the presence of an emulsifier and a polymerization initiator has been widely used in various, aqueous paints.
In this type of emulsion, fine vinyl resin particles are stably dispersed in an aqueous medium.
However, since a considerable quantity of surfactant or emulsifier are generally required for both purposes of securing a uniform dispersion of monomers in a reaction medium and a stable dispersion of thus formed microparticles in a dispersing medium, they are always remained in the emulsion causing undesirable decrease in water resistance of the formed coating.
To cope with the same, the so-called soap-free polymerization using no surfactant or emulsifier had been proposed by A. Homola, R. O. James, J. Colloid. Interface Sci. 59, 123 to 134 (1977), wherein a monomer having in its molecule an amino group and a monomer having a carboxyl group as acrylic acid, methacrylic acid or the like are copolymerized without using a surfactant or emulsifier to obtain an anphoionic resin latex. However, in this soap-free polymerization, since there is no surfactant in the reaction system, dispersion stability of thus formed latex particles is rather poor and therefore, it is unable to increase the latex solid content to a desired higher level. Furthermore, a mean diameter of thus formed resin particles is at most several hundreds nm and it is hardly possible to obtain the particles of much smaller size from the technical standview. Incidentally, the latex product obtained by A. Homola et al had a solid content of less than 10% and a mean grain size of more than 0.1.mu..
It is, therefore, an object of the invention to provide a stable vinyl resin emulsion containing no external surfactant of emulsifier, which is useful in an aqueous paint. A further object of the invention is to provide a stable vinyl resin emulsion containing ultra-fine resin particles in a higher solid concentration. An additional object of the invention is to provide novel vinyl resin microparticles which are very useful in paint and other areas.